Process of making dicyandiamid



Patented Feb; 22, 1927.

UNITED STATES" GEORGE BARSKY, OF NEW YORK, N. YQIASSIGNOR TO AMERICAN GYANAMID' COM- PANY, OF NEW YORK, N; Y., A CORPORATION OF MAINE.

i rnoonss or nxrfie DICYANDIAMIZD.

No Drawing. v {application filed .Tune 9,

This inventionrelates to a process of polymerizing certain types of organic compounds in such a manner that a maximum' yield of the desired product will be obtained, and the formation of objectionable by-products will be reduced to a minimum. The discovery is illustrated and particularly pointed out in i-the production of dicyandiamid from calcium cyanamidin a contin uous operation, and at the same time eliminating the common and objectionable side reactions which lead to the formation of ammonia, urea, melamine, etc, atT'the. ex-' pense of either the calcium cyanamide,.' the dicyandiamid, or both. It also"relate's to the discovery broadly of a COIIIIIEICMII method of selectively producing and recovering a pure material when the reactionwould normally yield a complex mixture. It also aifords a method of controlling the addition of reagents so that at all times the desired chemical equilibria will be main-. tained, and the reaction will progress in the desired direction. g Y.

The object of the invention is to provide a method that will be simple in its nature, comparatively easy to carry out and less costly to operate than those heretofore proposed. With these and other objects in view the invention consistsiri the novel steps and combinations of steps constituting the process, all as will be more fully hereinafter disclosed and particularly pointed out in .the claims.

In practicing my invention I may take 325 pounds of'calcium cyanamid whiclris added to about 975 pounds of water in a vessel provided with a stirring apparatus and means for controlling the temperature thereof. The addition is made in such a manner as to avoid local heating of the solution due to the heat of solution, fifltl'tlle temperature is kept below about C. to C. by stirring, cooling coils or in any ther manner. hen solution is substantially complete (about 90% of the calcium cyanamid in solution) it is filteredto remove insoluble material.

The resulting solution ofcalcium" acid cyanamid is then treated with a 10% solution. of sulphuric acid until it is just acid to thymolphthalein indicator QHj 9.6) keeping the temperature below C; after which the solution is filtered giving'a solution of free cyanamid. The temperature is phuric acid is then added to make the solu- 1923. Serial NO. 644,501.

tion slightly acidto methyl red (pl-1 5.0) to prevent decomposition of the diacyandiamid and the solution is filtered, if necessary,-after which it is evaporated at about 50$; C.1intil it begins to crystallize. The solutieniis cooled and filtered to recover the crystals of' dicyandiamid and the mother liquor may be reworked, all as is Well known in the art of evaporation.

Although in the above illustration I have referred particularly to the employment of sulphuric acid, I do not wish to be confined to the use of this acid as many others may be j suces'sfully substituted. I also do not wish to confine myself to the use of an acid at all as any material capable of maintainmg a correct hydrogen ion concentration in any manner whatsoever will accomplish the results. As an illustration of a method of this nature, I may add a so-called bufier, such as a mixture of boric acid and sodium borate or I may use a. buffer and an acid at the same time.

The preliminary treatment of the material may be varied to suit the conditions and to reduce the cost to a minimum. For example, I have described a method in which trations may be dispensed with, and that 100 .the acid may be added to the Water or to the lime nitrogenmixture,- under the proper control as before, until the cyanamid disappears. The solids may then be removed by filtration or decantation to permit of the 105 tion of the resulting filtrate. l It has been proposed to prepare recovervof the dicyandiamid by evapora -f diamld by extracting calcium cyanamid'withfi Water and treating the extract acidin and the decomposition oi." the dicyandiam-id amid. I have found that these processes either do not give good yields,-.or are so cumbersome in operation or (lillicult to carry out that it is unprofitable to employ them for the production of dicyandiamid.

In the production o'ldicyandiamid from cyanamid, other reactions may take place, both forming undesirable compounds and reducing the yield. These react-ions include the formation of ammonia, urea, melamine,

formed.

I have investigated the reactions tak ng place in solutions of cyanamid under vari-.

ous conditions and have found: 1-That the reaction whereby dicyandiamid is formed from cyananiid has an appreciable velocity at hydrogen ion concentrations between normal at temperatures between (1.. and

2-That at any definite hydrogen ion t ion concentration of, the solution.

tion is a typical reaction of the second order;

that is atany instant during the course of the reaction the "ate of cyanamid polymerization is proportional to the square of the eyanamid concentration existing at that instant.

3-T hat the yelocity of the reaction at any period varies withthe hydrogen ion concent 'ation-at that period, being a maximum at essentially 10 normal.

4 -That ata temperature of C. the decomposition of the dieyandiamid takes place at an appreciable rate when the hydrogen ion concentration is at and below 10 normal and that the lower the hydrogen ion concentration the greater is the rate of tie composition.

,5-- That the destruction of dicyandiamid at temperatures above 80 C. becomes appreciable when hydrogen ion concentrations are greater than 10* normal.

6--That the effect of a rise of temperatureis to increase the rate of polymerization essentially in accordance with the general rule that a 10 degreerise doubles the velocity of the reaction.

In a solution of cyanamid having a'hydro gen ion'eoncentration such that dicyandiamid is formed, the formation of dicyandiamid is accompanied by a decrease in the hydrogen This follows from the fact that cyanamid is 'a stronger acid than the dicyandiamid formed from it. This decrease in hydrogen ion concentration is further augmented by the factthat two molecules of cyanamid each containing two potential hydrogen ions, polynormal and 10' merizc to form one molecule of dicyandiamid containing one potential hydrogen ion.

Consequently,. the hydrogen ion eoncentration of a solution of cyanamid in which the formittion of (ll(? '2l.11tll2lllll is taking place is constantly changing. As a result of this change I have found that the rate of formation of dicyandiamid as well as the rate of other reactions involving cyanamid together with the rate of other reactions involring dicyandiamid are affected. -It follows, theretore, that by controlling the hydrogen ion concentration of the reacting solution, I can so control the reaction as to secure .the maximum formation of dicyandiamid. Further, I find that by causing the reaction to take place under conditions ofrhigh velocity I can largely avoid the formation of other cyanamid derivatives; and since I can' obtain a high reaction velocity without the range of dicyandiamid destruction, I canqalso secure high yields of dicyan'cliamid.

In the treatment of cyanamid I do not confine myself to the use of any particular salt. or solution ofthe same. My process applies to any solution however prepared. Nor do I confine myself to any particular acid, as any acid or other substance capable of bringing about and maintaining the correct degree of. hydrogen ion concentration for the purpose-in hand may be employed.

The essential feature of my invention is 'the maintenance and control of the hydrogen ion concentration, and the temperature at a point that will bcstsuit the purpose in hand. If a maximum yield is the object sought, then said concentration and temperature will be so chosen that the reaction will yield a maximum amount of the material desired with a minimum decomposition of the same and-the formationof a minimum of objectionable by-products.

If it is desired at any time to retard the reaction'or to cause a complete cessation for a certain period. it may be brought about by changing the hydrogen ion concentration to a point (2911* 5.0) at which the velocity of formation of dicyandiamid is practically nil. To again start the reaction it is simply necessary to bring the hydrogen ion con centration back to the proper point (pIP 9.6)." By this means one-may practically -stop the reaction at the close of the day and start it u a the next morning.

Itiis o vious that those skilled in the art may vary the details of the process as well as the method of controlling it without departing from the spirit of the invention, and therefore I do not wish to be limited to the abovev disclosure except as may be required by the claims.

What I claim is:

1. A method of controlling the trans formation pf calcium cyanamid into di-' cyandiamid which comprises mixin lime nitrogen with sufiicient water to disso ye the calcium cyanamid; addin dilute sulphuric acid until the hydrogen ion concentration substantially reaches l" normal; and gradually adding further amounts of acid to maintain this hydrogen ion concentration until a substantial portion of the cyanamid disappears, substantially as described. a

2. A method ofcontrolling' the transformation of calcium cyanamid into" dicyandiamid which comprises mixing lime nitrogen with suiiicientwater to dissolve the 'calcium cyanainid; adding dilute sulphuric acid until the hydrogen 1011' concentration substantially reaches -l0- normal; gradually adding further amounts of acid to maintain this hydrogen ion concentration until a tion of calcium cyan'amid into dicyandiamid ing to the which comprises treating lime nitrogen with suflicient water to dissolve out approximateoft'he cyanamid; filtering andaddfiltrate an amount or sulphuric acid sufficient to bring the hydrogen-ion concentration to substantially 10'? normal filtering off the solids; adding to the filtrate further sulphuric acid at a rate suflicient to substantially maintain this said hydrogen ion concentration until a material proportion of the cyanamid present disappears; adding acid'until the hydrogen ion concentration reaches substantially 10" normal;

" ion concentrationadding, dilute sulphuric acid to the agitated solution; maintaining said solution at a temand evaporating the solution preparatory to. obtaining the "desired stantially as described. l v

4. A method of controlling the trans- -iormation of a solution of cyanamid into dicyandiamid which comprises determining from time to time the degree of hydrogen agitating the solution;

perature of approximately C. until the hydrogen ion concentration reaeh'es' substantially 10"; normal; filtering ofl:' the solids; continuing the addition of. the acid .ally

dicyPandiamid; subwhile. maintaining substantially the same hydrogen ion concentration; maintaining said solution at a temperature of substanti- C. until the cyana'mid disappears; and recovering the dicyandiamid through evaporation of'the solution, substantially as described.- 5; A method of controlling the transformation of a solution of, cyanamid into'dicy andiamid which comprises'maintaining a hydrogen ion concentration between 10* and 10' -normal until a substantial amount of dioyandiamid is formed.

6. A method of controlling the transformation of a solution of cyanamid into dicyandiamid whichcomprises maintaining a hydrogen ion concentration between 10"- and 10*. normal and a temperature between 3U and 90 C. until a substantial amount of dicyandiamid is formed.

7. A method of controlling the transfor' mation of-a soultion etcyanamid into dicyandiamidxwhich comprises maintaining a 'hydrogen lon concentration between, 10"- and 10* normal and a temperature between.

30 and 90 C. until'a substantial amount of dicyandiamid is formed and. recovering the 8. A method of controlling the transformation of asolution of cyanarnid-into dicyandiamid which comprisesmaintaining a hydrogen ion concentration of about 10"-- normal and a temperature of about 50 (3-. until a substantial amount of dicyandiamid is formed. I

9. A method of controlling the -transformation of a solution of cyanamid into dicyandiamid which comprises maintaining a hydrogen ion concentration of about 10 normal and a temperature of about 50 C. untila substantial amountof dicyandiamid isformed and recovering the same.

10. A method of controlling the transformation of tyanamid vinto dicyandiamid which comprises maint-aining a suitable hydrogen ion concentration to form dicyana GEORGE BABSKY.

1 In testimony whereof I afiix my signature. 

